In recent years a plural color or full color image forming apparatus of the electro-photographic type, for example, laser color printers, there has been put into practical use a so-called in-line type image forming apparatus in which a plurality of photo-sensitive drums are arranged in a plane in conformity with respective colors arranged sequentially. Toner images of the respective colors are formed on respective photosensitive drums are successively super-imposed on a media, typically paper that is positioned on a transfer belt to thereby form a color image as the transfer belt and the media are advanced in a forward direction in the plane. The transfer belt is positioned around a plurality of rollers, each roller having its axis of rotation perpendicular to the plane in which the transfer belt moves as the color image is formed on the media.
U.S. Pat. No. 6,600,893 (“the '893 patent”) describes a full-color image forming apparatus, also referred to as a full-color printer, as an example of a conventional electrophotoprinting; color laser printer including a conventional in-line transfer belt assembly.
The image forming assembly is provided with four image forming portions or sub-assemblies, often referred to as cartridges, e.g., a yellow image forming portion or yellow cartridge, a magenta image forming portion or magenta cartridge, a cyan image forming portion or cyan cartridge and a black image forming portion or black cartridge. Each of the cartridges also includes drum-shaped electro-photographic photosensitive members, referred to as drums that function as image bearing members.
Each drum is negatively charged and driven or rotated at a pre-determined speed through use of a stepper motor assembly. Primary chargers function to uniformly charge the surfaces of the respective drums to a predetermined potential of negative polarity. Each cartridge contains the toner therein and, during operation causes the toner of each color to adhere to an electrostatic latent image formed on each drum to thereby develop the latent image as a toner image.
The transfer rollers as transferring means are disposed in respective transferring portions or zones so as to be capable of contacting with the respective drum with the intermediate transfer belt interposed there between.
The transfer belt is passed over two belt-conveying rollers. This transfer belt is formed of dielectric resin such as polycarbonate, polyethylene terephtalate, resin film or polyvinylidene fluoride resin film.
The toner image is transferred directly to the transfer belt through the transferring rollers with the media interposed there between the transfer belt and the drums, thus forming a color image with un-fixed, pre-melted toner powder. The media with the pre-melted toner powder then moves on to the fuser rollers, which in turn fuse the toner by means of heat onto the paper and thus fixing it.
The transfer belt apparatus is, usually, an easy to remove mechanism that has to be replaced once a certain amount of cartridges has been used or when it is damaged. Normally, if not damaged, the printer will notify the user when it is time to replace the transfer apparatus. On some printers, once the message appears, it is possible to reset the unit again. In some models, though there is no option to reset the printer and failing to replace the unit will end-up in inability to print. Prior experience shows that on the models that the transfer unit can be reset the printer can function with reasonable performance for a great deal of time without replacing the transfer unit.
Failure to replace the transfer unit for a long period of time might cause poor transfer efficiency thus poor print result. Moreover, excess use of the transfer unit might cause complete failure of the transfer belt, which might cause a permanent damage to the printer or the cartridges.